[英]TypeError: can't convert expression to float
I am a python newbie. 我是python新手。 I am trying to evaluate Planck equation using python. 我正在尝试使用python评估Planck方程。 I have written a simple program. 我写了一个简单的程序。 But when I give input to it is giving me an error. 但是,当我输入信息时,会给我一个错误。 can anyone hep me where I am going wrong? 谁能帮我解决我的问题? Here is the program and the error: 这是程序和错误:
Program: 程序:
from __future__ import division
from sympy.physics.units import *
from math import *
import numpy
from scipy.interpolate import interp1d
#Planck's Law evaluation at a single wavelength and temperature
def planck_law(wavelength,temperature):
T=temperature
f=c/wavelength
h=planck
k=boltzmann
U=2*h/(c**3)*(f**3)/(exp(h*f/(k*T))-1)
return U.evalf()
Input: I have imported the function as 'cp' and the input is as follows 输入:我已将函数导入为“ cp”,输入如下
value = (cp.planck_law(400,2000))
Error: 错误:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>`enter code here`
File "Camera_performance.py", line 14, in planck_law
U=2*h/(c**3)*(f**3)/(exp(h*f/(k*T))-1)
File "/usr/lib/python2.7/dist-packages/sympy/core/expr.py", line 221, in __float__
raise TypeError("can't convert expression to float")
TypeError: can't convert expression to float
It seem like you are mixing namespaces, since your are using from ... import *
. 似乎您在混合名称空间,因为您使用的from ... import *
。 You wanted to use sympy.exp()
but your code uses math.exp()
. 您想使用sympy.exp()
但是您的代码使用math.exp()
。 It is good practice to keep the namespaces separated, ie never use from ... import *
- it might seem like more typing at first, but will produce much cleaner easier comprehensible code in the end. 好的做法是将名称空间保持分离,即从不使用from ... import *
-乍一看似乎输入更多,但最终会产生更清晰易懂的代码。 Try: 尝试:
import sympy as sy
import sympy.physics.units as units
def planck_law(wavelength,temperature):
"""Planck's Law evaluation at a single wavelength and temperature """
T=temperature
f=units.c/wavelength
h=units.planck
k=units.boltzmann
U=2*h/(units.c**3)*(f**3)/(sy.exp(h*f/(k*T))-1)
return U.evalf()
# Test:
print(planck_law(640e-9*units.m, 500*units.K))
# Result: 1.503553603007e-34*kg/(m*s)
Your term h*f/(k*T)
isn't unitless, so you cannot pass it to exp()
. 您的术语h*f/(k*T)
不是无单位的,因此您不能将其传递给exp()
。 Doesn't make sense in a physical context, either ;-) 在物理环境中也没有意义;-)
You can get a result if you divide it by K
and m
: 如果将结果除以K
和m
则可以得到结果:
exp(h*f/(k*T)/K/m)
but that surely makes no sense. 但这肯定没有任何意义。 It's just to make the program run (into nonsense). 只是为了使程序运行(胡说八道)。
I guess you will have to check your formula and find out how you really want to compute the value you want to pass to exp()
. 我猜您将不得不检查您的公式并找出您真正想要如何计算要传递给exp()
。
EDIT: 编辑:
As Pascal pointed out, you are just missing the units for the arguments you pass. 正如Pascal指出的那样,您只是缺少传递的参数的单位。 Try it with: 尝试使用:
planck_law(400e-9*m,2000*K)
Returns: 返回值:
3.20224927538564e-22*kg/(m*s)
When you call your function, you need to pass units to the temperature and wavelength argument. 调用函数时,需要将单位传递给温度和波长参数。 Calling cp.planck_law(400*meters,2000*K)
gives the expected 1.15133857387385e-33*kg/(m*s)
. 调用cp.planck_law(400*meters,2000*K)
得到预期的1.15133857387385e-33*kg/(m*s)
。
The problem arose with the exponential function, which, rightfully, expects to receive a dimensionless argument. 问题是由指数函数引起的,该函数理所当然地希望收到一个无量纲的参数。 Since the arguments you were passing did not include units, Sympy treated them as dimensionless floats, rather than a temperature and a length, as required. 由于您传递的参数不包含单位,因此Sympy将其视为无量纲浮点,而不是根据需要的温度和长度。
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